Q: I own a 1993 Ford 1720 diesel tractor. Previously, I have always replaced the battery with a unit from the dealer. The dealer would have me believe that their batteries are the only ones built to withstand the vibrations and demands of a diesel. Is there any downside or possibility of damage to the electrical system (normal 12V) by using a battery of equal or slightly higher cold cranking amperage purchased from a Walmart?

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A: Short answer: no, not really.

The dealer is partly correct; diesels and trucks in general vibrate more, and could potentially damage a battery by making the lead plates inside crack.

So, I would look for a truck-rated battery, which will have a more robust interior construction.

Better yet, look for an AGM (absorbed-glass-mat) type of battery. This construction has the electrolyte soaked into an inorganic blotter between the plates. The plates are stuffed tightly into their individual cells in the battery case, and can't move, or break. Because the hydrogen that's electrolyzed out of the electrolyte is captured and recombined with oxygen to make water, there's never any need to add distilled water.

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Of course, AGM batteries are somewhat more expensive than a battery from Wal-Mart, but one should outlast even the truck battery the dealer wants to sell you. And should be around the same price, because the truck dealer has a substantially higher markup on parts. Shop around

Q: I have a 1996 Nissan pick-up, the ABS lights in the dash came on and now I have very little brake pressure. I've looked the brake lines and the fittings over and see no leaks, I've also added fluid to the almost empty reservoir and still no pressure. Is there a quick fix or any other solution this problem? Being a weekend mechanic this situation has me stumped any information would be greatly appreciated.

A: This a classic letter, one I get nearly every day.

You let the level of brake fluid in the reservoir get far too low. When you applied the brakes hard enough, the master cylinder sucked in an air bubble when you released the brake pedal. You've refilled the reservoir, but the air is still in there. The air is compressible: the brake fluid is not, which is why the pedal is spongy--you're simply compressing the air bubble, which is pretty much the same thing as putting a big, soft, spring between the pedal and your foot.

You'll need bleed the brakes properly to remove the air. And I'd flush the system thoroughly at the same time. This simply means bleeding the brake calipers and wheel cylinders not only until the air stops bubbling through, but until the fluid coming out of the bleeder screws is fresh and clear.

Q: My 2003 Chevrolet Impala has brake rotors that rust in the driveway. Dealer has turned them to remove rust which in turn means that they have shortened life expectancy. Are you aware of any Technical Service Bulletins on this matter? My wife's 2003 Nissan Altima sits on our driveway just as much but does not have rusting rotors-let me guess, GM is sourcing cheap imported rotors to keep their costs down and pass the repair bills to their customers.

A: I don't think it's the rotors. Brake rotors on cars and trucks are virtually all made with the same alloy of gray cast iron. Which rusts, pretty much overnight when it's damp or rainy.

Usually, that's not a big deal. The light film of rust scrubs off with the first brake application or two. If your car is rusting too much, enough that the brakes are pulsating because they're out of true, it's not being driven enough. It should take a couple of months of storage to get to the point where the discs don't run true and need to be machined.

I have two thoughts: the Nissan's brake pads are composed of some compound that leaves a hydrophobic (water-hating) coating behind, You could try switching to a different pad.

Or maybe it's just parked in an area that doesn't get as much rain.

Q: On a 1993 Ford Pickup, 1/2 ton, XLT, 2 wheel drive, the engine dies when stopped for traffic signals and hesitates when accelerator is touched. The Check Engine light comes on. I have already changed throttle control valve. What would you recommend?

A: I'd recommend getting a mechanic to use a scan tool and find out why the Check Engine light is on. And don't swap out any more expensive parts until you find out what's actually wrong. A can of fuel injection cleaner and a brief cleaning of the throttle body wouldn't hurt, either.

Q: I really enjoyed your article about fixing modern cars, but you said something that I have a question about. You mentioned multiple places for online car manuals, and I was wondering what are some of those sites?

A: Motorbooks.com or Amazon.com for printed manuals.

Alldatadiy.com for online manuals.

Other manuals can sometimes be found online via Google for specific vehicles.